The invention is based on an electrical machine, in particular a brushless synchronous motor.
In conventional, permanent magnet-excited, brushless synchronous motors that are designed as internal rotor motors, the permanent magnets that generate the excitation field in the working air gap between the rotor and stator are embodied in the form of shell segments affixed to the surface of the rotor. If it is optimized, a synchronous motor of this kind has a low cogging torque and a low degree of torque undulation, which is very favorable for certain uses of the motor in which a very smooth torque is required. The disadvantage of this motor is the high production cost, due in particular to the production of the shell-shaped permanent magnets, which must be ground in order to produce the shell shape.
In order to reduce the production costs, brushless synchronous motors have therefore been developed in which the permanent magnets embedded in the rotor are “buried” in it (EP 1 028 047 A2). The “buried” permanent magnets are mostly rectangular and can be easily cut from a large block of permanent magnet material, which reduces costs in comparison to a shell-segment magnet. Even when optimized, such a brushless synchronous motor with “internally buried” permanent magnets, also referred to as an IPM motor, tends to have a significantly higher cogging torque and higher degree of torque undulation than a comparable motor with shell-shaped permanent magnet segments on the surface of the rotor.